(1) Field of the Invention
The present invention relates to a thread regulating apparatus in a sewing machine having a plurality of thread regulators each including a pair of tension discs for holding a thread therebetween and applying tension to the thread.
(2) Description of the Prior Art
A thread used for stitching by a needle or a looper is usually drawn from a bobbin on which the thread is wound, and is passed through a needle hole. Since the needle moves at high speed in a stitching operation, the thread tends to be drawn in an unrestricted manner. This gives rise to the problem of a defective finish with loose stitches in the resulting product.
This problem of loose stitches is solved by applying a suitable tension to the thread at an intermediate position between the bobbin and the needle in a direction to arrest its movement toward the needle. FIG. 1 shows an example of a known thread regulator for applying such a tension to the thread. The regulator comprises a pair of tension discs 103 and 104 loosely mounted on a shaft 102 rigidly connected to a main machine frame 101. A spring 105 and a pressing screw 106 are mounted on the shaft 102 outwardly of one of the tension discs 103. This tension disc 103 is pressed on the other disc 104 through a compressive force of spring 105 by tightening the screw 106. Thus, tension is applied to the thread held between the two tension discs 103 and 104.
In a sewing machine having only one stitching needle, it is easy to apply the tension by means of the thread regulator and maintain an upper thread and a lower thread in a well-balanced relationship.
However, in the case of a sewing machine having a plurality of stitching needles or loopers for looping an edge and a plurality of thread regulators for applying tension to respective threads, it requires a great amount of skill to apply the tension to the threads in a balanced way, which renders a sewing operation difficult. There is another problem that, even if the pressing screw 106 is tightened to a selected degree, the tension could change with variations or secular changes in the urging force of spring 105.